1. Field of the Invention
The present invention relates to massage devices which apply pressure to the body. More particularly, the invention is in the class of medical devices which utilize cyclic pressure to aid blood circulation in the limbs of a human body.
2. Related Art
Medical devices that apply cyclic pressure to a person's legs, arms and/or feet are very old and well-known in the art. Many have employed pulsating pads or plungers for improving circulation. Others have used hydraulic and pneumatic bladders for the same and for many other purposes. The shapes, sizes, and composition of such bladders and pads are widely varied, depending largely on their particular application.
Man has known the fundamental principle of most cyclic compression devices for thousands of years. They are merely a more recent embodiment of the old art of massage, which  has been used to stimulate circulation since prehistory. Use of mechanical devices to effect the massaging action is obviously more recent, but has a clear history of more than 150 years.
Full understanding of the mechanism involved in this form of improving blood flow is more recent but has not fundamentally changed the devices used to accomplish this result. Veins are now known to contain a series of one-way check valves along their length. Thus, when pressure is applied, compressing a vein, the fluid expelled therefrom can only proceed in the direction of normal circulation. When such compression is relaxed, the vein returns to its normal circular cross-section, and the flow of blood into the vein is increased until it reaches its normal state of back pressure. Repeating this cycle in a cyclic fashion thus increases blood flow in the normal direction of circulation.
Such compression/decompression cycles occur naturally in humans as part of the action of the muscles and flexure of the limbs. It has been known for many years that the arch of the foot includes a large venous plexus (or group of veins). It is also known that this venous plexus is compressed during normal walking or running, thereby stimulating circulation. This efficient circulation aid is a marvelous design by our Creator, as its effect is greatest when the leg muscles (the largest muscles in the body) are in action and need the oxygen supplied by enhanced circulation.
For these and other reasons, the foot has long been known as an effective site for applying cyclic pressure. For instance, many devices such as Massator's “PediPulsor” improve circulation by positioning a pulsating, dome-shaped pad in the arch of the foot. Many others have targeted the arch of the foot with flexible pneumatic chambers. A partial sampling of such pneumatic devices that target the arch of the foot includes Japanese utility model No. 47-10392, U.S. Pat. No. 4,614,180 issued to Gardner et al. and U.S. Pat. No. 4,941,458 issued to Taheri. 
Many others have long recognized that the foot contains veins that can be massaged or pumped to provide better circulation. Some examples are: L. E. Corcoran, who states in his U.S. Pat. No. 2,880,721 issued Apr. 7, 1959 that massaging the soles of the feet “promotes a beneficial degree of circulation;” Richard Dillon, M.D., whose Journal of Vascular Diseases, January 1986 report entitled “Treatment of Resistant Venous Stasis Ulcers and Dermatitis with the End-Diastolic Pneumatic Compression Boot” on treatment of circulation-impaired patients states “compression boot therapy enjoys a 173 year history;” and P. Gaskell, M.D. and J. C. W. Parrot, M.D., whose Surgery, Gynecology and Obstetrics, April 1978 report entitled “The Effect of Mechanical Venous Pump on the Circulation of the Feet in the Presence of Arterial Obstruction” shows a high level of understanding of the process of venous pumping with pulsed air by stating “[w]e have found that the boot covering the foot alone is simpler, less cumbersome, and gives a greater reduction of venous pressure than either a large cuff which covers the whole calf or a boot which includes the calf and the foot.”